Carnis - I rely on other people's reported experience regarding online BB. For example, Porkus Maximus on the Nurgle thread says:
"Like I said, a lot of online players have a strong "pixel hugger" mentality and will concede at the first sign of blood on the pitch. Unfortunately the 51spp rule for star players is not in effect because it would kind of suck to have a bunch of players quit if you lost internet connection for some reason, however this does make conceding a viable method of team preservation. Since concessions are much more common place, killer teams end up with ridiculous treasuries up in the millions which means that spiralling expenses rarely affect them and if they wish to concede against an even more brutal team, then they can afford to. Alternatively you also have people who are attempting win streaks to attain higher rankings and they'll concede as soon as the dice turn sour, they're not interested in sticking around if they think they've already lost. Concede, delete the team and start again.
This is the unfortunate problem of introducing Blood Bowl to a MASS online audience, who don't seem to have the "Blood Bowl spirit" that you'd expect from tabletop players. Thankfully there are plenty of successful private leagues where this kind of behaviour is frowned upon."
I hear similar reports from friends of mine who have played online BB. I agree with you, however, that there should be little difference between private leagues in tabletop and online, provided the same ruleset is used.
But it would appear that a significant proportion of online games does not fall into this category. That's all.